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Date:   Wed, 31 May 2023 15:20:32 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
Cc:     Christoph Hellwig <hch@lst.de>, Qu Wenruo <quwenruo.btrfs@gmx.com>,
        Naohiro Aota <Naohiro.Aota@wdc.com>,
        "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: new scrub code vs zoned file systems
Message-ID: <20230531132032.GA30016@lst.de>
References: <20230531125224.GB27468@lst.de> <546fad79-f436-c561-8b9b-0d9a7db09522@wdc.com>
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On Wed, May 31, 2023 at 01:10:55PM +0000, Johannes Thumshirn wrote:
> So it looks like we're calling btrfs_lookup_ordered_extent() with a NULL
> inode.
> 
> This actually makes sense as the current scrub code does not have an inode
> in the bbio so:
> 
> btrfs_simple_end_io(bio)
> `-> btrfs_record_physical_zoned(btrfs_bio(bio))
>     `-> btrfs_lookup_ordered_extent(bbio->inode, ...)
>         `-> tree = &inode->ordered_tree;
>             spin_lock_irqsave(&tree->lock, flags); <--- BOOM
> 
> We don't really need the inode in the zoned code, but the ordered_extent.
> 
> I've just quickly skimmed over "add an ordered_extent pointer to struct 
> btrfs_bio v2" but didn't find anything that adds it for scrub writes as well.

That is correct, but as far as I can tell it is just the symptom.

The underlying issue is that the scrub code has no zone awareness at
all, and just tries to rewrite sectors in place.  The old code OTOH
tried to always migrate the entire BG (aka zone).

> 
> 
---end quoted text---